Sol-gel film is a film formed by undergoing the steps of forming a coating solution having an oligomer by allowing a hydrolysis and polycondensation reaction of an alkoxide compound to proceed, then applying this on a substrate, and then drying, etc. Since it is possible to introduce into sol-gel film a functional material capable of optically, electrically and chemically generating functions, the use and the proposal are conducted in various uses. In particular, a sol-gel film having a film thickness exceeding 0.5 μm has high usefulness, in view of providing optical and chemical functions.
On the other hand, in view of practical use of sol-gel film, it is an important study task to make the film higher in wear resistance and hardness. It is disclosed in Patent Publication 1 that a film superior in flatness and superior also in wear resistance is obtained by a dipping method by adjusting the amount of a surfactant to be added to 10-30 weight % of an organic silicon compound, 30-60 weight % of a metal oxide fine particle sol, 10-50 weight % of a water-soluble organic solvent, and 0.1-5 weight % of a curing catalyst.
Furthermore, Patent Publication 2 discloses a coating composition characterized by containing a partial condensate of an organic silicon compound formed of 100 parts by weight of trialkoxysilane and 130 parts by weight of tetraalkoxysilane, and silica fine particles. Furthermore, Patent Publication 3 discloses a forming solution, in which silicon alkoxide concentration in terms of SiO2 exceeds 3 mass % and is less than 9 mass %, and which is capable of forming a hard silica-based film by adjusting concentrations of water and acid.
Patent Publication 4 discloses a coating composition containing a copolymer obtained by hydrolysis and polycondensation of 100 parts by weight of alkylalkoxysilane and 0.1-20 parts by weight of tetraalkoxysilane, and silica fine particles, and surface flatness of the film is discussed therein.
On the other hand, means for applying a coating solution on substrate has a great influence on qualities such as hardness, optical distortion, film thickness, etc. of sol-gel film. Although properties of a coating solution impose a great limit on the means for applying the coating solution on substrate, many of conventional techniques dealing with coating solutions for sol-gel films do not raise questions about the application method. In many conventional techniques, it is in fact an assumption to apply a coating solution by using means such as dipping coating method, spin coating method, flow coating method, spray coating method, etc.
Therefore, a coating solution capable of obtaining a sol-gel film of high quality, in terms of not only hardness and transparency, but also external appearance, optical distortion, film thickness, etc., even by an application means capable of application with no equipment, such as hand application, is of great importance from industrial applicability of the above-mentioned sol-gel film. Furthermore, this application means is of great importance from the viewpoint of saving resources too, since transfer efficiency of the coating solution to substrate is high, thereby hardly wasting resources.
Although Patent Publication 5 discloses a coating agent that contains a complex in which an organic polymer compound and a metal oxide are chemically bonded and that is capable of spray coating by hand application or manual operation, there is much room for improvement with respect to wear resistance and weather resistance of a film to be formed, and a further study is necessary.    Patent Publication 1: Japanese Patent Publication Application 2002-228989    Patent Publication 2: Japanese Patent Publication Application 01-306476    Patent Publication 3: Japanese Patent Publication Application 2006-111851    Patent Publication 4: Japanese Patent Publication Application 08-283661    Patent Publication 5: Japanese Patent Publication Application 2001-316635